The invention relates to a method and apparatus of evaporating materials in a vacuum evaporator by bombarding the material to be evaporated with electrons from a low-voltage arc discharge.
For the evaporation by means of an electron beam, thre are known so-called electron beam evaporators with a hog cathode. In such evaporators, the power density required for the evaporation is obtained on the material to be evaporated by accelerating a relatively low electronic current (for example, of 1 A) with a relatively high voltage (for example, 10 kV), This produces a beam having a small cross section which, frequently, is directed onto the evaporative material through a magnetic field, along an arcuate path. Such an electron beam entails only a small activation (i.e. ionization, excitation, dissociation) of the residual gas and the vapor in the evaporator. This is due to several reasons: (1) the low current intensity; (2) with high energy levels, the effective cross sections are small; (3) higher residual gas pressures cannot be permitted, since they cause flash-overs in the acceleration path and sputtering of the hot cathode. However, to obtain layers of higher quality, an activation of the vapor of the evaporative material or of the residual gas in the evaporation space would be very desirable in many vapor deposition processes.
Further known are electron beam evaporators with a hollow cathode. Distinction is made between cold and hot hollow cathodes (see, for example, C. T. Wan, D. L. Chambers and D. C. Carmichael, The Journal of Vacuum Science and Technology, Vol 8, No. 8, p. VM 99, 1971). Unlike normal electron beam evaporators, these two kinds can be operated at pressures above 10.sup.-4 mb; the desired current-voltage characteristic, however, is furnished only by the hot hollow cathode. It delivers high currents at a low operating voltage (for example, 100 V, 100 A) and thus ensures an effective activation of the residual gas and the vapor. Hot hollow cathodes, however, are hard to ignite and, therefore, require an additional ignition device. Moreover, at the same time, the cathode material is sputtered and deposited on the substrates to be coated, as contamination.